The amount of profit depends on the exact person we are talking about.
Traders use different strategies while trading on forex. Some people prefer safety to high profits, but there are also very agressive traders who use high leverages which brings big risks.
The main thing, from my point of view, is to know what you are doing, to have realistic expectations of the deals you make and calculate the risks.
Again it is hard to say how much time someone needs to understand trading and himself, but the more efforts and time you devote to trading, the better you trade and the higher profits you get.